Field of the Invention
The invention relates to a steam turbine with a steam inlet region, an exhaust-steam region and a blading region surrounded by a turbine housing and disposed axially therebetween. The invention relates furthermore, to a method for cooling a steam turbine having a turbine housing.
A method and device for cooling an idly running steam or gas turbine are described in German Patent 324 204. For carrying out the cooling, an ejector connected to the steam flow conduit via a valve is specified. By the ejector, steam is sucked away through the inflow conduit in the opposite direction to the normal direction of flow. The steam sucked away may be tapped or exhaust steam from a further turbine as well as wet or saturated fresh steam.
U.S. Pat. No. 3,173,654 relates to a steam turbine with a high-pressure part turbine and a double-flow low-pressure part turbine that is run in the stand-by mode. To avoid overheating the turbine blades, there is provided a cooling system, via which-water under high pressure is injected out of the condenser into the part turbine by a multiplicity of conduits both in the low-pressure part turbine and in the high-pressure part turbine. The water evaporates completely and, since the vacuum pumps are in operation, is returned into the condenser again. The quantity of injected water is regulated as a function of the temperature in the part turbines, for each injection conduit, separately in each case, via a corresponding valve.
Patent Abstracts of Japan, Vol. 008, No. 073 (N-287) of Japanese Patent Application No. 58-220907 describes a steam turbine plant with a low-pressure part turbine, a high-pressure part turbine and a medium-pressure part turbine. A condenser is connected to the low-pressure part turbine. The exhaust-steam conduit of the high-pressure and low-pressure part turbine is connected to a vacuum pump in order to avoid thermal tensions and thermal expansions during cooling. Air is forced through the high-pressure and medium-pressure part turbine via the pump opposite to the flow direction of the action steam, which, in normal operation of the turbine, flows through it. The air comes, in the case of the high-pressure part turbine, directly from the condenser and in the case of the medium-pressure part turbine, it also comes indirectly via the low-pressure part turbine from the condenser. Air enters the condenser via a vacuum breaker. The air inlet therefore lies at the end of the flow path of the action steam far downstream of the high-pressure and medium-pressure part turbine, namely in the condenser of the low-pressure part turbine.
The two publications mentioned above therefore relate in each case to the cooling of steam turbines running idly or running in the stand-by mode. In these instances, cooling takes place solely via steam which either is supplied directly or occurs as a result of evaporating water. The above two publications therefore relate to a steam turbine in a state in which externally generated heat is discharged, the heat occurring as a result of friction in a turbine running at an operating rotational speed, of, for example, 3000 revolutions per minute. If the heat were not discharged, the temperature in the steam turbine would be well above the operating temperature.
In a steam turbine, particularly a high-pressure turbine or a medium-pressure turbine with preceding intermediate superheating, temperatures of up to and above 500.degree. C. occur during operation in the power mode. In the course of operation in the power mode, for example under full load, which may last a few weeks or months, the turbine housing as well as the turbine rotor and other turbine components, such as the fresh-steam valve, quick-closing valve, turbine blade, etc., are heated to a high temperature. After the steam turbine plant as a whole has been shut down, the turbine rotor of each turbine can continue to be rotated at a reduced rotational speed for a predetermined period by a rotation device and the steam atmosphere can be evacuated via an evacuation device. So that maintenance or checking work and, if appropriate, retrofitting work can be carried out as soon as possible after the steam turbine has been shut down, it may be desirable, under certain circumstances, to cool the steam turbine as quickly as possible. While at the same time adhering to predetermined limits for differences in expansion which occur between the turbine rotor and, for example, the turbine housing.